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How to calculate the circuit breaker current at home?

By:Nader Updated:August 19,2020 20:32PM

The selection principle of the home circuit breaker is still based on the maximum operating current. That is, the maximum adjustable current of the selected MCB is greater than or equal to the working current calculated from the total power.

Multiply the total current of the connected load by 1, 2 to select the master switch, the load power is 220 volts and 1 kilowatt about 4.5 amps. The air switch installed in the home may be changed due to the household appliances used, and there needs to be a margin. It can be selected according to the current carrying capacity of the total incoming line. For example, the total opening uses 40 to 63 amps, the branch lighting is 10 amps, the air conditioning branch is 20 amps, electric water heaters and The kitchen socket is divided into 30A. It depends on the electricity consumption of each road. The three-story canteen can select the main air switch for 1.2 times the total current of all electrical equipment.

1. The selection principle of household electric air switch is: choose according to power supply capacity. For example, a 30A meter, then the 30A total air switch is the most reasonable. According to household electric power calculation, the total circuit breaker can be lower than the current value of the watt-hour meter, but should not be greater than the current value of the watt-hour meter.

2. When the family chooses the air switch, it is not suitable for the main air switch to use the leakage switch, otherwise, once a certain electrical appliance leaks, all the indoor power will be cut off, which is extremely inconvenient. The correct choice should be: use leakage protectors for socket switches and air conditioner switches, and not use leakage switches for lighting switches and general air switches.

3. When the MCB is selected, the capacity (ie: current) of each opening shall not exceed the current of the total MCB, otherwise the abnormal phenomenon of "overstepping" trip protection will occur.

Total power of your electrical appliances:

The family has 2 air conditioners (3P) 4500, 1 water heater (2000 watts), 1 electric porcelain stove (1600), 1 computer 500, 1 refrigerator 600, 2 TV 300.


The total power calculation formula: P=UIcosφ and I=P/Ucosφ

P is the circuit power

U is line voltage, single phase is 220V

cosφ is the power factor of inductive load, generally 0.8

Your line current:


The maximum setting current of the MCB you choose is 63A, which is greater than the total operating current of 52A, which conforms to the selection principle.

In theory, this calculation is correct, but there is still a problem. Generally, the household capacity is only 5KW, and it is impossible for them to work at the same time. According to the above calculation method, the switch cannot play the role of overload protection. The entrance line of building residents is generally 2.5mm2, and basically it cannot reach this level after cutting corners. If it can reach the standard, that is, the current is 32A. Therefore, it is very dangerous if all the spare switches are installed. Line, it is recommended to calculate according to the household capacity, choose from 20A-32A.